Processing and processing Errors of complete

denture (1)

• Lecturer of prosthetic dentistry and implantology- Faculty of dentistry –Minia University

First and above all, thanks to merciful ALLAH, who enable me to complete this work.

Introduction

WAXING UP OF TRIAL DENTURE BASE.

What is waxing up ?

•The contouring, of the trial denture base’s polished

surface , by adding wax to reproduce the original form of

tissues.

WHY DO WE PERFORM WAXING UP?

1- to provide, support to oral structures.

2- natural appearance to the denture base simulating natural gums.

3- shape the flanges to correspond to the inner surface of the cheeks and

tongue.

4- seal the border spaces between the trial denture base and the cast.

HOW DO WE PERFORM WAXING UP?

How do we perform waxing up?

Face bow index for clinical remounting

Denture processing

• Separation of the waxed up denture from the articulator

• Articulator without any remounting plates.

• The mounting plaster is carefully splitting from the cast.

• The articulator is placed on cloth to avoid damage of the trail denture.

• Split the junction between the mounting plaster and the cast with help of

wax knife and plaster mallet.

• After separation, the cast’s soaked in water

• Save the plaster mounting as it will be used to reposition the cast on the

articulator after the dentures are processed.

Disarticulation

Disarticulation

Flasking:

Is the process of investing the cast with the waxed denture in a flask to make a sectional

mold that is used to form the acrylic resin denture base.

The flask consist of four pieces :

The base (which

contain the cast.)

Round knockout plate.

The top half of the flask. Lead.

• Check out flasks from dispensing when you’re ready to flask.

• Record flask numbers.

• Note differences in upper and lower flasks.

Procedure:The following procedure is applied to both maxillary and mandibular dentures

Preparation of the cast:

Try the casts in the bottom half of the flasks.

At least ¼ inch of space should exist between the occlusal surfaces andincisal edge of the teeth and the top of the flask.

Trim the casts if necessary but you must retain the index groove.

Soak the casts and waxed dentures in water for a few minutes.

Soak casts and mounts to facilitate removal.

1. Coat the inner surface of the flasks with vaseline.

2 .First pour:

This pour is made of a mix of plaster of paris.

Test the cast in its place.

Spatulate a heavy mix of plaster and stone and fill the lower half of the flask till about

one-third.

Seat the cast until the land area is flush with the rim of the flask.

Flasking:

• Add stone to flask first. Seat cast completely to bottom of flask

1. Coat the inner surface of the flasks with vaseline.

2 .First pour:

Remove excess plaster, smooth the remaining

*No undercuts should be present in the plaster

* Be sure that all the portion of the metal rim are free from any plaster

For the lower cast , bring a small amount of plaster in the tongue space to eliminate

the undercut in the region of the retromylohyoid fossa

Allow the investment to set then proceed to the second investment

Flasking:

3.Second pour:

Position the second part of the flask and ensure that the two halves are contacting metal to

metal.

Place a thin film of vaseline on the surface of the set stone in the lower half of the flask.

Position the second part of the flask in place.

Spatulate a thin mix of half plaster and half stone and pour it over the teeth from one corner

of the flask. Avoid entrapping air in the mix.

Bring the stone to the occlusal surface of the invested teeth leaving exposed occlusal

surface of the posterior teeth and the incisal edge of the anterior teeth.

4.Thid pour:

Apply separating medium on the set plaster and stone (i.e. second pour)

Complete the investment using a mix of stone . Stone will resist more pressure

than a mix of plaster and stone.

Fill the flask with the mix, place the lead of the flask in position, some stone should

pass through the holes of the lead.

Allow the stone to set at least one hour before wax elimination.

Wax elimination

Wax elimination ( Dewaxing ) or Boil out is madeto remove the wax in the wax

pattern, so that a mold space is created for acrylic to fill in.

Put the flask in boiling water (100 C ) for 5 min.

Before placing the flask into the water bath, the clamp should be loosened.

Dewaxing is done to just soften the wax and not melt it which can be easily

removed from the mold when the flask is opened.

Boiling out• The flask is placed in boiling water for 6 minutes

• Shortened boilout results in pulling teeth from second pour.

Wax elimination

Open the flask through the provided openings.

Carefully remove the softened wax. All teeth should remain in the top half of

the flask

If any of the teeth have been pulled loose they should be replaced in position.

Using hot water flush out all the remaining wax and any residue that may be

present.

• Flask opened by inserting plaster knife between the 2 halves of the flask

• Wax denture is removed from the mold as 1 piece.

Wax elimination

Flush the flask again with hot water to which a detergent has been added.

Use a small paint brush to thoroughly clean the stone and teeth from any residues of wax.

The final flushing is done is done with clean hot water to remove all traces of the detergent

solution.

It is essential to remove all wax residue since acrylic resin will not adhere to a surface coated

with wax.

Any residual wax will contaminate the acrylic resin and prevent bonding between the teeth

and the denture base.

• Opened flask is washed by hot water until the remaining wax is removed

Breakage of the plaster during separation may be due to any of the following

A rough surface or undercuts on the plaster in the first section.

Insufficient thickness of plaster covering the teeth.

Insufficient or incorrectly applied separating medium.

Teeth too near the edges of the flask.

Plaster not completely set before separation.

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Stand the flask on its side and allows it to dry .

while the mold is still warm paint all the portions of the exposed stone with a

separating medium.( tin-foil substitute such as alginate solution). This is done to

make the surface of the mold nonabsorbent to avoid penetration of the liquid

acrylic resin (monomer) into the stone during processing.

If liquid acrylic resin penetrates the mold surface the finished denture will have

a crust of acrylic resin and stone or plaster. This layer has to be removed during

finishing. The result is improperly contoured and hence an unaesthetic and poor

fitting denture base.

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Allow the first coat of separating medium to dry then apply a second coat and

allow it to dry.

The separating medium should be placed around the teeth and over the surface of

plaster or stone.

The procedure should produce a smooth and shiny mold surface.

Roles of separation medium :

- To prevent the passage of water from gypsum to resin

- To minimize the passage of monomer to the plaster

- To facilitate separation of the flasks

Heat cure acrylic is used , Mixing of powder and liquid (polymer /monomer) is

mixed according to manufacture instruction , usually 10cc of monomer , and

30cc of polymer will be enough to pack an average- sized denture. ( 1:3 ) M / P.

When the material reaches the dough stage, it is ready for packing.

Packing is introduction of denture base resin material into the mold cavity.

The powder liquid mixture should be packed into the flask at the dough stage.

PACKING

TRIAL PACKING

TRIM THE EXCESS.

Curing (polymerization) :

- After final closure the flasks are kept at room temperature for 30 to 60 min . this

is known as bench curing.

- Purpose of Bench curing: Permit an equalization of pressures throughout the

mold space

Curing cycle: It is polymerization cycle. The curing cycle selection depends on

the thickness of the resin.

Curing (heating) cycle: -

1- long cycle:

Heat the flask in water at 60-70°C for 9 hours.( long curing ) –

2- Short cycle :

Heat the flask at 74°C for 90 minutes, then at 100°C for 60 minutes. ( short curing

Long cycle

1 hour to reach 70 °C

9 hours at 70 °C

Short cycle

1.5 hours to reach 74 °C

1 hour at 100 °C

FINISHING AND POLISHING

FINISHED DENTURE

Sincerely :

Dr. Hussein A. Hady Hussein